The invention relates to an immersion device for collecting a slag sample and measuring a molten metal parameter, as well as a method for collecting a slag sample and measuring a molten metal parameter.
In most molten metal refining processes, particularly processes for making steel, a molten slag is produced forming a layer above the molten metal. Molten slag has a lower density than the molten metal. Because of this, the molten slag floats and accumulates above the surface of the molten metal that is commonly located within a processing vessel. The slag provides for essential metallurgical functions such as the absorption of certain elements desired to be removed from the molten metal or the creation of a reaction environment in which elements such as carbon are oxidized in the molten slag and released as a gaseous byproduct of the reaction.
In the metal making industry, it is important to monitor the chemical and/or metallurgical composition of the refining slag in order to effectively monitor the molten metal processing, to compare initial calculated chemistry to actual composition to update charge mass and material balance models and to efficiently collect and timely analyze the slag in order to particular properly control the metal refining process.
A traditional method for obtaining a sample of metal refining slag from a molten metal bath in a processing vessel is to immerse a metal object, such as a pipe, a metal spoon, a metal chain or the like into the slag for a predetermined relatively short period of time. A layer of the molten slag is chilled onto the cooler metal object so that upon removal of the metal object from the processing vessel, the solid slag may be conveniently broken away from the metal object, collected and promptly analyzed using known analytical methods and techniques.
This method has the disadvantage of an unsecured sample composed of the broken smaller pieces which at times can be mixed at the collection location with broken bits of slags of a previous process batch. Securing the frozen slag collecting process, such as taught in U.S. Pat. No. 6,370,973, employs a funnel 4 to direct the liquid slag 31 through a mold inlet 3 to a sample chamber 2 with a cooling plate 5 to obtain a slag sample after removal from the sample chamber 2.
It is also common in the metal producing industry to monitor various other qualities of the molten metal in a processing vessel such as temperature, temperature of solidification, dissolved oxygen and to obtain physical samples to ascertain other component contents. Many different types of devices or probes have been developed and used for this purpose, such as disclosed in U.S. Pat. No. 7,832,294. Typically, a measuring head containing sensing elements is mounted upon a carrier tube, typically a cardboard tube, and immersed into the molten metal bath. The cardboard tube supports the measuring head and/or samplers allowing the sensors and/or samplers to be inserted into the molten metal at a desired depth below the molten slag to obtain the necessary data and/or physical sample. When a sample of the slag floating upon the molten metal is desired, it has been known to extract a physical sample into an inflow conduit located on the side of the hollow carrier tube, such as taught by U.S. Pat. Nos. 5,415,052 and 9,176,027. Alternatively, it has been known to secure generally cylindrical metal shapes to the cardboard tube such as metal tubes or metal coils at a stationary position, such as in U.S. Pat. No. 5,435,196 or 7,621,191. In this manner, when the probe body is inserted or immersed into the molten metal bath for making the required measurement at the tip during refining, a sample of the slag can be simultaneously obtained at the side and recovered when the probe body is removed from the metal bath.
While these methods of obtaining slag samples can be useful in some applications, it is commonly difficult to use because it requires to adapt the immersion process to the exact location of the slag and its depth, so that the metal object used for collecting the sample of the slag is, in fact, maintained in the slag layer and does not pass through the slag into the molten metal below the slag layer.
A further problem is related with slag sample collection from a converter for producing steel. A converter is a furnace for producing steel from iron as well as scrap iron, steel and/or iron with impurities. Molten iron is added to the scrap iron, iron and/or steel with impurities. A high pressure stream of oxygen and particularly powdered lime is blown through the mixture, causing chemical reactions and removing some of the carbon from the iron. The amount of carbon removed from the iron determines the quality or grade of steel produced. This part of the process is monitored carefully until the percentage of carbon is reduced to the correct level according to the type of steel required. The slag of a converter, i.e. converter slag, is continuously in motion, contains gas components and has a fluidity that varies widely during the converter process. Therefore, slag sample collection is generally difficult and sometimes not even possible with devices configured for slag from a refiner; i.e. refiner slag.
International Patent Application Publication No. WO 2011/047846 describes this issue and the particular difficulties during taking slag samples from a converter due to the different properties of converter slag and the special converter conditions compared to all other slag sampling processes, such as, for example, refiner slag. Page 2, lines 5 to 13 of International Patent Application Publication No. WO 2011/047846 describes that a serious problem with taking slag samples from a converter is that the slag because of poor fluidity will not flow into a sample chamber with a small inlet channel as used in taking slag samples from for instance pig iron. For that reason, the sample chamber has to have a large inlet opening. With a sample chamber having a sectional area which is determined by the inner sectional area of the probe used with the sub-lance system to take a sample, the size of the inlet opening is in the range of at least half of that sectional area to equal to the sectional area of the sample chamber. However, with a large inlet opening it is a problem to keep the slag in the sample chamber.
Nowadays, a probe for collecting a slag sample from a steelmaking converter is typically a multifunctional measuring probe that is not only able to collect slag samples, but also comprises one or more measuring elements for measuring properties of the molten metal during only one single immersion process. If obtaining only converter slag samples, one could select a wide inlet opening with a comparatively big diameter for reliable converter slag collection as taught in International Patent Application Publication No. WO 2011/047846 and U.S. Pat. No. 6,370,973.
In particular, it is targeted to collect a slag sample with at least a temperature measuring unit in the same sensor. The sensor is immersed in the bath by means of a sublance system. The vessel is a converter for steelmaking, mostly operated with a top blowing lance and bottom gas stirring.
However, conventional immersion probes have at least a thermocouple and as such there is typically only limited space available on the measuring head of such multifunctional measuring probes as, for example, illustrated in U.S. Pat. No. 9,176,027. This available space at the immersion end on the measuring head is particularly not enough for arranging the wide inlet openings, as taught in International Patent Application Publication No. WO 2011/047846 and U.S. Pat. No. 6,370,973, and, at the same time, all thermal mass at the measuring head can disturb the accuracy of the bath temperature measurement.
The contents of the cited documents are incorporated by reference herein. The above described features known from the prior art can be combined alone or in combination with one of the below disclosed aspects and embodiments of the present invention.